Field of the Invention
The present invention relates to a control device of a variable stiffness mechanism having dielectric elastomers that elastically deform according to an applied voltage.
Description of the Related Art
A dielectric elastomer is characterized in that, when a voltage is applied thereto, the dielectric elastomer is compressed by Maxwell stress in the direction of an electric field produced by the applied voltage. Further, the stiffness or the like of the dielectric elastomer (hereinafter referred to simply as “the elastomer” in some cases) can be controlled to a predetermined desired state by variably manipulating the voltage applied to the elastomer. Due to the characteristic, the elastomers have been used in a variety of technical fields in recent years.
For example, Japanese Patent Application Laid-Open No. 2003-174205 (hereinafter referred to as “Patent Document 1”) proposes a device in which a sheet-like elastomer is interposed between two members, which are mutually relatively displaceable, and the voltage applied to the elastomer is manipulated thereby to enable the stiffness between the two members to be changed.
In a variable stiffness mechanism configured to have elastomers interposed between two members, the stiffness between the two members can be changed over an extensive range by interposing a plurality of elastomers between the two members and manipulating the voltage applied to each of the plurality of elastomers.
Meanwhile, in order to properly control the stiffness of this type of variable stiffness mechanism, it is frequently desired to make it possible to acquire the amount of the relative displacement between the two members or a state amount closely related thereto.
In this case, it is conceivable to, for example, directly measure the amount of the relative displacement between the two members or the elastic deformation amount of the elastomers that corresponds to the amount of the relative displacement by using a displacement sensor, such as a distance sensor, or the like. However, the displacement sensor is required to be disposed in the vicinity of the elastomers or the two members, thus frequently leading to structural restrictions. Further, the elastomers can flexibly deform in shape in response to an external force, so that it is generally difficult to measure, with high reliability, the elastic deformation amount of the elastomers by using a displacement sensor.
On the other hand, the elastomers are electrical insulators, so that the elastomers function as capacitive elements. Further, the electrostatic capacitance of the elastomers as the capacitive elements are highly correlated to the thicknesses of the elastomers (the thicknesses in the direction in which an electric field acts), or the values of geometric dimensions, such as areas or the like. Further, the electrostatic capacitance of elastomers can be estimated from electrical detection values, such as current values, so that a system for measuring the electrostatic capacitance is less likely to be subjected to structural restrictions.
Hence, the electrostatic capacitance of the elastomer could be measured (estimated) as a state amount closely related to the amount of the relative displacement between the two members.
In this case, it is desired that the processing of variable control of the stiffness of the elastomers between the two members and the processing of estimating the electrostatic capacitance can be carried out in parallel without mutual interference.